python解析xml库lxml-马育民老师

# 概述

lxml是python的一个解析库，解析HTML和XML，支持 **XPath解析方式**，底层由C语言实现，解析效率非常高

官网：
https://lxml.de/

官方api：
https://lxml.de/api/index.html

# 安装
```
pip3 install lxml
```

测试：
```
from lxml import etree
```

# 解析xml文件

### 初识
xml文件内容：
```
<?xml version='1.0' encoding='utf-8'?>
<student age="20" sex="男">李雷</student>
```

python代码
```
from lxml import etree

tree=etree.parse("/Users/mym/Desktop/python/2.xml")
print(type(tree))

#将xml内容转成bytes返回
content=etree.tostring(tree,encoding="utf-8")
print(content)
```
执行结果：
```
<class 'lxml.etree._ElementTree'>
b'<student age="20" sex="\xe7\x94\xb7">\xe6\x9d\x8e\xe9\x9b\xb7</student>'
```
**注意：**
`type(tree)`返回类型是`lxml.etree._ElementTree`

### 获取根节点
```
root = tree.getroot()
print(type(root))
```
执行结果：
```
<class 'lxml.etree._Element'>
```
**注意：**
`type(root)`返回类型是`lxml.etree._Element`

### 获取标签名
```
print("标签名：",root.tag)
```
执行结果：
```
标签名： student
```

### 获取标签文本
```
print("标签内容：",root.text)
```
执行结果：
```
标签内容： 李雷
```
### 获取标签属性
```
print("age属性：",root.attrib["age"])
print("sex属性：",root.get("sex"))
```
执行结果：
```
age属性： 20
sex属性： 男
```

### 遍历

通过`for in`进行遍历

xml内容如下：
```
<?xml version='1.0' encoding='utf-8'?>

<students>
    <student age="20" sex="男">李雷</student>
    <student age="19" sex="女">韩梅梅</student>
</students>
```
python代码：
```
from lxml import etree

tree=etree.parse("/Users/mym/Desktop/python/2.xml")
root = tree.getroot()

for item in root:
    print("标签名:",item.tag)
    print("  姓名:",item.text)
    print("  age:",item.attrib["age"])
    print("  sex:",item.get("sex"))
```

执行结果：
```
标签名: student
  姓名: 李雷
  age: 20
  asex: 男
标签名: student
  姓名: 韩梅梅
  age: 19
  sex: 女
```

# 解析xml字符串

### 方法一
使用`etree.XML()` 方法
```
from lxml import etree

xml="""<student age='18'>李雷</student>
"""

tree=etree.XML(xml)
print(type(tree))

# 转成bytes
content=etree.tostring(tree,encoding="utf-8")
print(content)
```
执行结果：
```
<class 'lxml.etree._Element'>
b'<student age="18">\xe6\x9d\x8e\xe9\x9b\xb7</student>'
```
**注意：**
`type(tree)`返回类型是`lxml.etree._Element`

### 方法二
使用`etree.fromstring()` 方法
```
from lxml import etree

xml="""<student age='18'>李雷</student>
"""

tree=etree.fromstring(xml)
print(type(tree))
content=etree.tostring(tree,encoding="utf-8")
print(content)
```
执行结果：
```
<class 'lxml.etree._Element'>
b'<student age="18">\xe6\x9d\x8e\xe9\x9b\xb7</student>'
```
**注意：**
`type(tree)`返回类型是`lxml.etree._Element`

### 解析带有编码的xml字符串
```
from lxml import etree

# 注意此处有encoding
xml="""<?xml version='1.0' encoding='utf-8'?>
<student age='18'>李雷</student>
"""

tree=etree.XML(xml)
```
会报错：
```
ValueError: Unicode strings with encoding declaration are not supported. Please use bytes input or XML fragments without declaration.
```

**解决：**
带有encoding编码的xml字符串，解析时，需要先转成bytes
```
from lxml import etree

xml="""<?xml version='1.0' encoding='utf-8'?>
<student age='18'>李雷</student>
"""
# 需要先转成bytes
xml=xml.encode("utf-8")
tree=etree.XML(xml)
print(type(tree))
```

感谢：
https://www.cnblogs.com/zhangxinqi/p/9210211.html#_label1
https://blog.csdn.net/oXiangDuiNiShuo1/article/details/51864503

原文出处：http://malaoshi.top/show_1EF504JL0LdB.html